function pop(file) {
    var x_size = window.screen.width;
    x_size = x_size - 600;
    x_size = x_size / 2;
    x_size = Math.round(x_size);

    var y_size = window.screen.height;
    y_size = y_size - 580;
    y_size = y_size / 2;
    y_size = Math.round(y_size);
    y_size -= 50;

    popupwindow = window.open(file,"pophelp","scrollbars=yes, toolbar=no,location=no,directories=no,status=no,menubar=no,width=600,height=580, left=" + x_size + ",top=" + y_size);
    popupwindow.focus();
    return false;
}